In the field of dentistry, restoration of a patient's tooth or teeth that have, for example, been affected by caries generally includes the replacement of the natural tooth substance by an artificial substance. For larger restorations, pre-finished dental restorations or prostheses are commonly used to replace at least a part of the tooth or teeth.
Dental restorations or prostheses are often made as a two or more component configuration, with the individual components providing different characteristics for the restoration. For example, a frame may provide excellent structural support, and a facing may provide excellent aesthetics. The frame generally is a supporting structure for the dental restoration that provides mechanical stability and usually comprises an interface by which the restoration can be affixed to a prepared tooth of a patient. The facing provides for pleasing aesthetic characteristics that gives the restoration the shape and appearance of natural teeth. In addition, both the frame and the facing are shaped to fit well with the adjacent and opposed teeth in a patient's mouth.
In the recent years ceramic materials have been widely used for making high-quality dental restorations because of their good physical, aesthetic and biological properties. These restorations are often manufactured by an automated process, which typically includes:                capturing data representing the shape of a patient's teeth, for example by scanning a plaster model of the patient's teeth or alternatively by scanning the actual teeth in the patient's mouth;        designing the shape of a frame based on the captured data using software, such as computer-aided design (CAD) software; and        manufacturing the frame to correspond to the designed shape, for example, by an automated Computer Numerical Controlled (CNC) machine.        
There are approaches to integrating the steps of capturing, designing and manufacturing in a Computer Integrated Manufacturing (CIM) system. An exemplary CIM system for making frames for dental restorations is available from 3M ESPE AG (Seefeld, Germany) under the trade designation LAVA™.
Although such CIM systems would allow the manufacture of an integrated dental restoration (frame and facing together, in the example mentioned above), it is difficult to provide a single ceramic material that provides both the necessary structural durability and good aesthetics. Therefore the CIM system is normally used to manufacture the frame from a ceramic material that provides the required mechanical durability without regard to its aesthetic properties, after which a final layer or facing is applied to the frame to provide the necessary aesthetic properties. A facing of this type is very often manually prepared by skilled dental technicians, for example by manually applying several layers of a polymeric material or a glass-ceramic material, to provide the appropriate color, translucency, and other properties.
Another common method for manually preparing a facing is the “press over” technique. A frame is manufactured as described above, and manually covered with a wax layer or “wax-up” 300 with an outer surface that corresponds to the desired final shape of the tooth. That wax-up is used to form a pattern for a mold. The mold is then heated in a furnace so that the wax is burned off, and the frame remains as a core in the mold. The space between the core and the interior of the mold is then filled with a molten glass-ceramic material that is, for example, obtained from melting a ceramic pellet in channel or previously molten and poured into the channel, where it flows around the frame and fuses with the frame to form the facing. The restoration may then be removed from the mold, polished as necessary, and provided to the dentist for application to the patient's tooth.
Other methods of preparing dental restorations are described, for example, in DE 10 2005 034 803 A1, and DE 19 944 130 A1.
DE 10 2006 033 794 B3 describes a indirect route by milling a wax veneer and subsequently investing, burn-out the wax and pressing the veneer porcelain in the lost form.
WO 2008/009495 is directed to a set of elements for producing a dental prosthesis comprising a framework and one or more model parts for defining parts of the outer contour of a veneer for the framework. The model parts are typically made of wax and are burnt during the production of the dental prosthesis.
Although the current approaches for manufacturing of dental restorations may provide a variety of advantages, there is still a desire for a method of manufacturing an entire high-quality dental restoration in a cost efficient manner.
If possible, the dental restoration should be durable and have less defects or cracks.